1. Field of the Invention
The invention is in the field of photocopy machines and copy/duplicator machines which utilize fusing means to fix toner particles upon copy paper passing therethrough. The invention particular relates to logic circuitry adapted to control the turn-on and turn-off of the fusing element at appropriate times in relation to various machine modes of operation.
2. Description of the Prior Art
Over heating of the fuser station in copier/duplicator machines has long been a problem in the prior art, and many control circuits have been developed to maintain the temperature of the fuser station within predetermined limits. Particular heat problems arise in fusing stations because of the necessity to maintain a relatively high temperature to achieve proper fusing or fixing of the toner particles onto the copy paper while, at the same time requiring that the overall temperature within the fusing station be maintained relatively low so that feed rollers do not pick-up toner particles and produce "ghost" images. It is also important to maintain the temperature of fuser station itself within a finite temperature range to achieve uniformity of toner fusion on the copy paper. Control circuits to achieve such ends are illustrated in Lawes et al., U.S. Pat. No. 3,505,497 and Traister U.S. Pat. No. 3,735,092 wherein various warm-up time periods are utilized and finite temperature ranges are maintained by the use of thermostats, thermistors and the like. It has also been the practice in the prior art to control heating and minimize power to the fuser by triggering the fuser only upon the approach of the copy paper to the fusing station as illustrated by the Mindell et al. U.S. Pat. No. 3,219,794. As indicated by the above patents, full power fuser turn-on voltages are utilized to control the temperature by regulating the time interval at which the voltage is applied. Alternate approaches however, utilize a variable voltage to the fuser element in attempting to optimize fuser operation. For example, applying an initial high voltage to the heating unit to achieve a fast warm-up is shown in the Crumrine et al. U.S. Pat. No. 2,852,651; varying the heating temperature as a function of the copy paper travel speed is taught by Hopkins U.S. Pat. No. 3,588,445; and providing a plurality of different heating levels within the fuser is shown by Hutner U.S. Pat. No. 3,745,304.
While the various control circuits of the prior art help to reduce over-heating, none of these techniques provide an adaptive fuser control circuit for regulating fuser timing operations with respect to different modes of the copier/duplicator operation. Such multiple mode copier/duplicator machines may utilize, for example, both fixed and movable optical system and have large document copying capabilities (18 .times. -inches) as well as chain feed and multiple copy modes. An example of such machines is described in detail in copending applications, Ser. No. 367,996, filed June 7, 1973, and Ser. No. 528,163 filed Nov. 29, 1974, (D/73383C). In machines which operate in both chain feeding and large document copying (LDC) modes, it is often a problem to control the fusing element to achieve the proper fusing temperatures and yet prevent overheating and power surges. In these multiple mode machines, it is desirable to control the full power fuser turn-on at an appropriate time with respect to each separate mode of operation of the copier/duplicator.
Additionally, when the large document copying mode is used, it is desirable to regulate the fuser element in relation to the size of the copy paper employed.
In the large document mode of operation, an additional input power surge problem occurs in systems utilizing a zero to full power fuser turn-on such as that shown in the aforementioned Mindell patent. For example, current surges associated with 1150 watt fusers can typically run to 100 amps and thus cause power supply fluctuations and transients which may lead to pole slippage in the drive motors. Drive motor slippage in turn leads to poor copy quality as large document feeding modes typically have exposuring, development, transfer and fusing operations being conducted simultaneously. In effect, the copy paper is large enough so that parts of the paper are still being exposed, developed and transferred when the leading edge of the copy paper reaches the fusing station and full power to the fuser is required.